1. Field of the Invention
The present invention relates in general to implements for injecting liquid fertilizers into the ground and more specifically relates to such implements having a circular array of spokes for penetrating the ground and supplying fertilizers thereto.
2. Description of the Prior Art
A variety of implements have been utilized for injecting liquid fertilizers into the soil of a field for agricultural purposes. One of the older types of such implements includes a plurality of spaced apart knives that break the ground and provide narrow slits into which the liquid fertilizer is dispersed. Although implements providing a knife application of fertilizer have proven to be an effective means for efficiently distributing fertilizer in a field, the tractive energy required for such application is relatively substantial in comparison to the application of fertilizer by a spray operation. For this reason, a variety of spoked wheel type application implements have been developed as alternatives to subsurface knife application implements.
In contrast to the knife application of fertilizer that requires a continuous ground disrupting operation, the spoked wheel implements provide an application of fertilizer into the soil at spaced intervals to be essentially as energy efficient as fertilizer spraying devices. However, prior to the present invention spoked wheel fertilizer applicators have not been widely accepted on a commercial basis. Either they are needlessly complex as exemplified by the structures disclosed in U.S. Pat. Nos. 3,602,166; 3,649,061; and 3,025,806, or they do not have means for preventing the loss of fertilizer into the atmosphere as exemplified by the device disclosed in U.S. Pat. No. 2,876,718.
During the early 1980's, Iowa State University became involved in developing an improved spoked wheel fertilizer applicator. Several embodiments of the type of spoked wheel applicator developed by personnel at Iowa State University are disclosed in Paper No. MCR 83-114 presented to the American Society of Agricultural Engineers Mar. 11, 1983. The basic construction of the Iowa State University embodiments included a wheel with a rotary valve in its hub to sequentially provide fertilizer to spokes extending outwardly therefrom so that dispersement of fertilizer from the spokes primarily occurs only when the spokes are ground engaged. Although the embodiments developed by Iowa State University are an improvement over earlier devices, the rotary valve construction they include is deficient in its sealing capabilities and its operational performance. Such deficiencies in the Iowa State University embodiments result from the use of a metal axle and a nylon axle bearing to form the rotary valve structure to provide durability of the valve. However, such valve construction does not permit for the clearance between the axle and the bearing to be sufficiently small to provide proper sealing without making the valve susceptible to seizure during operation due to expansion of the valve components as a result of heat or moisture absorption. Furthermore, such embodiments had problems with spoke breakage because the hub was formed of steel and did not provide a resilient mount for the spokes.
The present invention provides an improved spoked wheel applicator that efficiently and economically injects fertilizer into the soil by the use of a rotary valve that not only has sufficiently small clearance between its components to provide optimum sealing operation of the valve, but also is constructed to reduce the possibility of structural damage and seizure of the applicator due to heat.